HIV-associated dementia (HAD) is an AIDS-defining illness mediated by activated, infected brain macrophages. Determining the host factors that participate in viral replication in activated macrophages is thus important for understanding the pathogenesis of HAD and for developing better therapies. Annexin 2 is a cellular membrane-binding protein that binds to p55 Gag, the HIV protein responsible for viral assembly and budding, in activated macrophages that produce infectious virus but not in non-activated macrophages that have a late stage block in the viral life cycle. The role of Annexin 2 in HIV assembly and budding will be investigated in the current proposal. Specific Aim 1 is to map the Annexin 2 binding site on p55Gag using site-directed mutagenesis guided by structural similarities between p55Gag and a cellular binding partner of Annexin 2. Specific Aim 2 is to determine how macrophage activation regulates Annexin 2 to facilitate its interaction with p55Gag. Specific Aim 3 is to investigate the functional role of Annexin 2 in HIV assembly and budding by comparing the replication of wildtype virus in macrophages to that of virus with mutated p55Gag unable to bind Annexin 2.